A semiconductor device having a silicon single crystal as a substrate goes through an oxidization process for forming an oxide film on the surface of a silicon substrate (silicon wafer), a diffusion process for diffusing impurities, a low pressure CVD (LPCVD) process for forming a silicon nitride film, a polycrystal silicon film (polysilicon film) under reduced pressure and the like, and has a very small circuit formed on the silicon wafer. Semiconductor production facility called diffusion equipment, an LPCVD equipment and the like are used for these processes. Each of these equipment is composed of a furnace part into which a plurality of silicon wafers are inserted and which heats the silicon wafer main body to high temperature, a gas introduction part for supplying a reactive gas into the furnace, an exhaust part and the like, and a number of silicon wafers can be simultaneously processed (batch processing) therein. FIG. 5 shows an example of a vertical type of LPCVD device.
In FIG. 5, a CVD device 10 is provided with a heater not shown at an inner circumferential surface of a furnace body 12 so that an inside thereof can be heated and maintained at a high temperature, and the CVD equipment is also connected to a vacuum pump not shown so that the inside can be pumped down to 10 Torr or less. The inside of the furnace body 12 is provided with a process tube 14 formed of a high purity quartz and silicon carbide (SiC).
A boat pedestal 18 is provided at a center portion of a base 16 covered with the process tube 14, and a wafer boat 20 in a vertical rack shape formed of SiC, quartz, or the like is placed on this boat pedestal 18. A number of silicon wafers 22 to form semiconductor devices such as a large scale integrated circuit (LSI) and the like are held with appropriate spaces between them in a vertical direction of the wafer boat 20. A gas introduction pipe 24 for introducing a reaction gas into the furnace and a thermocouple protecting tube 26 containing a thermocouple for measuring the temperature inside the furnace are placed at the sides of the wafer boat 20.
In the CVD equipment 10 constituted as above, a number of silicon wafers 22 are placed inside the furnace via the wafer boat 20. The pressure of the inside of the furnace is reduced to 100 Torr or less, the inside of the furnace is heated to a high temperature of, for example, 800° C. to 1200° C., and a carrier gas such as H2 and a reaction gas (raw material gas) such as SiCl4 are introduced into the furnace via the gas introduction pipe 24, whereby a polycrystal silicon film (polysilicon film) and a silicon oxide film (SiO2) are formed on the surface of the silicon wafer 22.
In the CVD device 10 as described above, a plurality of monitor wafers 30 are placed to mingle with the silicon wafers 22 at appropriate positions in the vertical direction of the wafer boat 20 to check the state of particles attached to the silicon wafer 22 and to check whether a film of predetermined thickness is formed on the silicon wafer 22 and the like. An Si single crystal wafer with surface roughness of about Ra=0.25 nm is generally used for a monitor wafer which is used to perform management of the film thickness of the formed thin film, particles and the like as described above. Though very flat surface as described above is obtained with the silicon single crystal, the conventional monitor wafer cannot be reused by washing the film with acid or the like when a polysilicon film or a silicon oxide film is formed, and it is thrown away after one use, which makes it very uneconomical. Consequently, SiC wafers, which are excellent in anticorrosion against nitric acid and the like, facilitate removal of deposits caused by etching, and can be repeatedly used for a long period of time, receive attention.
On the other hand, SiC has high hardness, then it is difficult to produce an ultra-flat surface. Polishing with use of a diamond abrasive grain is generally performed, but it easily gives a scratch damage onto the wafer surface by the abrasive grain or the SiC itself which is fallen away. Concerning the surface cleanness, there exists the problem of impurities mixing in this grinding process.
With the prior SiC polishing technique, it is not possible to produce an SiC monitor wafer having an ultra-flat and clean surface at low cost. For example, with the design rule of 0.13 μm in mind, it is necessary to detect a particle (dust) of at least 0.1 μm. However, with the SiC polishing technique corresponding to volume production of the present situation, the average roughness is about Ra=20 nm, and therefore it is confirmed that the particle detection cannot be performed with this surface roughness.
The present invention is made in view of the above-described problem of the prior art, and has its object to provide the SiC monitor wafer production method which can make a surface flat until the particle detection becomes possible.